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Abstract:

An optical instrument with temperature-related focal length variations
compensation mechanism is provided herein. The optical instrument
includes: a housing within a bore of the optical instrument, wherein the
bore and the housing have each a distal end and a proximal end; a set of
lenses located on a common optical axis and affixed within the housing,
wherein the set of lenses is associated with a specified focal length for
each specified temperature; and a temperature compensation member
connecting the distal end of the housing to the distal end of the bore of
the optical instrument, wherein the temperature compensation member
comprises one or more sections whose thermal expansion coefficient and
length along the optical axis are selected such that for a specified
range of temperatures, the expansion of the temperature compensation
member along the optical axis compensates for a change of the focal
length of the lenses.

Claims:

1. An optical instrument comprising: a housing within a bore of the
optical instrument, wherein the bore and the housing have each a distal
end and a proximal end; a set of lenses located on a common optical axis
and affixed within the housing, wherein the set of lenses has a specified
focal length for each specified temperature; a temperature compensation
member connecting the distal end of the housing to the distal end of the
bore of the optical instrument, wherein the temperature compensation
member comprises one or more sections whose (i) thermal expansion
coefficient and (ii) length along the optical axis are selected such that
for a specified range of temperatures, the expansion of the temperature
compensation member along the optical axis compensates for a change of
the focal length of the set of lenses.

2. The optical instrument according to claim 1, wherein one section of
the temperature compensation member is made of aluminum and wherein
another section of the temperature compensation member is made of an
amorphous thermoplastic polyetherimide material.

3. The optical instrument according to claim 1, wherein the temperature
compensation member has an average thermal expansion coefficient and a
length along the optical axis such that for each temperature within the
specified range, a change of the focal length is compensated by an
inverse change of the length of the temperature compensation member.

4. The optical instrument according to claim 1, further comprising a
sensor located at the focal length of the set of lenses, within the bore.

5. The optical instrument according to claim 1, wherein the housing is
sealed so that the set of lenses is air and humidity protected.

6. The optical instrument according to claim 1, wherein the specified
range of temperatures includes at least -20.degree. and +20.degree.
Celsius.

7. The optical instrument according to claim 1, wherein at least one of
lenses is humidity sensitive.

8. The optical instrument according to claim 1, wherein the bore further
comprises linear bearings configured to facilitate movements of the
housing within the bore along the optical axis.

9. The optical instrument according to claim 1, further comprising a
stopper attached to the temperature compensation member, and wherein the
stopper is located such as to limit the displacement of the set of lenses
in at least one direction along the optical axis.

10. The optical instrument according to claim 9, wherein the stopper is
located in a predefined location relative to the set of lenses so as to
enable displacement of the set of lenses in at least one direction along
the optical axis only to a certain point.

11. The optical instrument according to claim 9, wherein the stopper is
further configured to apply a force so as to reduce the displacement of
the set of lenses along the optical axis.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a non-provisional application claiming priority
from Israeli Patent Application No. 217165, filed Dec. 22, 2011, which is
incorporated herein in its entirety.

BACKGROUND

[0002] 1. Technical Field

[0003] The present invention relates to optical instruments and more
particularly, to optical instruments with temperature compensation
mechanism for focal length variations.

[0004] 2. Discussion of the Related Art

[0005] Optical instruments tend to suffer from focal length variation due
to changes in the temperature of the ambient. This is usually because the
optical indices of the lenses tend to change over temperature.
Additionally, the geometry of the lenses may further change due to
temperature variation and so does the focal length of the set of lenses.

[0006] Several solutions for the temperature-related focal length
variation problem are known in the art. FIG. 1 shows one such solution,
in which optical instrument 10 includes, for example, one set of lenses
20A-20F within optical instrument 10 that has an image sensor 60 affixed
thereto. Lenses 20A-20F are all affixed to identical members of
temperature compensation 50A and 50B. Temperature compensation members
50A and 50B may be comprised each of two or more portions of different
materials selected due to their respective temperature expansion
coefficient. Specifically, the length of each one of the portions and the
materials are selected so that the any change in the focal length of
optical instrument 10 due to changes in the geometry of lenses 20A-20F
due to temperature change is compensated by the expansion of temperature
compensation members 50A and 50B. In this manner, within a range of
temperatures, the effective focal length of optical instrument 10 remains
the same.

BRIEF SUMMARY

[0007] One aspect of the invention provides an optical instrument with
temperature-related focal length variations compensation mechanism. The
optical instrument includes: a housing within a bore of the optical
instrument, wherein the bore and the housing have each a distal end and a
proximal end; a set of lenses located on a common optical axis and
affixed within the housing, wherein the set of lenses is associated with
a specified focal length for each specified temperature; and a
temperature compensation member connecting the distal end of the housing
to the distal end of the bore of the optical instrument, wherein the
temperature compensation member comprises two or more sections whose (i)
thermal expansion coefficient and (ii) length along the optical axis are
selected such that for a specified range of temperatures, the expansion
of the temperature compensation member along the optical axis compensates
an increase of the focal length of the set of lenses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a better understanding of embodiments of the invention and to
show how the same may be carried into effect, reference will now be made,
purely by way of example, to the accompanying drawings in which like
numerals designate corresponding elements or sections throughout.

[0009] In the accompanying drawings:

[0010] FIG. 1 is a schematic diagram illustrating an optical instrument
according to the existing art;

[0011] FIG. 2 is a schematic diagram illustrating an improved optical
instrument according to some embodiments of the present invention; and

[0012] FIG. 3 is a schematic diagram illustrating yet another embodiment
of the improved optical instrument according to some embodiments of the
present invention.

[0013] The drawings together with the following detailed description make
apparent to those skilled in the art how the invention may be embodied in
practice.

DETAILED DESCRIPTION

[0014] With specific reference now to the drawings in detail, it is
stressed that the particulars shown are by way of example and for
purposes of illustrative discussion of the preferred embodiments of the
present invention only, and are presented in the cause of providing what
is believed to be the most useful and readily understood description of
the principles and conceptual aspects of the invention. In this regard,
no attempt is made to show structural details of the invention in more
detail than is necessary for a fundamental understanding of the
invention, the description taken with the drawings making apparent to
those skilled in the art how the several forms of the invention may be
embodied in practice.

[0015] Before explaining at least one embodiment of the invention in
detail, it is to be understood that the invention is not limited in its
application to the details of construction and the arrangement of the
components set forth in the following description or illustrated in the
drawings. The invention is applicable to other embodiments or of being
practiced or carried out in various ways. Also, it is to be understood
that the phraseology and terminology employed herein is for the purpose
of description and should not be regarded as limiting.

[0016] FIG. 2 shows an optical instrument with temperature-related focal
length variations compensation mechanism. Optical instrument 100
includes: a housing 110 within a bore of optical instrument 100, wherein
the bore and the housing have each a distal end and a proximal end.
Optical instrument 100 further includes a set of lenses 112A-112E located
on a common optical axis and affixed within housing 110. Specifically,
set of lenses 112A-112E is associated with a specified focal length for
each specified temperature. Optical instrument 100 further includes a
temperature compensation member 150 connecting the distal end of housing
110 to the distal end of the bore of the optical instrument 100.

[0017] Specifically, temperature compensation member 150 comprises two or
more sections (e.g., 150A and 150B) whose (i) thermal expansion
coefficient and (ii) length along the optical axis are selected such that
for a specified range of temperatures, the expansion of temperature
compensation member 150 along the optical axis compensates an increase of
the focal length of the set of lenses 112A-112E.

[0018] The inventor has discovered, based on a series of experimentations,
that for a specific set of lenses 112A-112E, optimal results for
temperature compensation were achieved in a case in which one section
(e.g., 150A) of the temperature compensation member was made of aluminum
and another section (e.g., 150B) of temperature compensation member 150
was made of the ULTEM amorphous thermoplastic polyetherimide (PEI)
material. It has been discovered that the combination of these two
materials each having different thermal expansion coefficient yields, in
carefully selected length, an average thermal expansion coefficient that
corresponds with the change in the focal length of the set of lenses
112A-112E.

[0019] Put formally, for a temperature compensation member of length l,
and a set of lenses of a focal length f, the two sections of the
temperature compensation member are selected such that for each
temperature T within the temperature range of T0 and T1 the
change in the length of the temperature compensation member Δl
equals the change in the focal length Δf.

[0020] Consistent with some embodiments of the invention, the temperature
compensation member 150 has an average thermal expansion coefficient and
a length along the optical axis such that for each temperature within the
specified range, an increase of the focal length is compensated by a
similar increase of the length of the temperature compensation member.

[0021] Consistent with some embodiments of the invention, the optical
instrument includes a sensor 140 located at the focal length of the set
of lenses 112A-112E, within the bore. The sensor may be any imaging
device configured for one or more spectral ranges such as visible light
and IR radiation.

[0022] Consistent with some embodiments of the invention, housing 110 may
be air tight or sealed so that the set of lenses is air and humidity
protected. This feature may be particularly advantageous in cases in
which one or more of the set of lenses 112A-112E is made of materials
that are vulnerable and easily affected by humidity.

[0023] Consistent with some embodiments of the invention, optical
instrument 100 includes an attaching/detaching means (not shown here)
connecting the distal end of the bore to the temperature compensation
member 150. The attaching/detaching means is usable or detaching the
temperature compensation member for calibration purposes. For calibration
purposes, housing 110, together with temperature compensation member 150
connected thereto, can be placed within a controlled oven in which the
expansion of the temperature compensation member 150 is precisely
measured so that the desired length may be achieved.

[0024] Consistent with some embodiments of the invention, the optical
instrument includes the specified range of temperatures includes at least
-60° and +60° Celsius. The optical instrument may be
designed with a temperature compensation mechanism for larger or smaller
temperature ranges.

[0025] Consistent with some embodiments of the invention, the bore further
comprises linear bearings configured to facilitate movements of the
housing within the bore along the optical axis. Advantageously the linear
bearings substantially reduce the friction between the housing and the
bore so that the operation of the temperature compensation mechanism
disclosed herein is facilitated. This feature makes optical instrument
100 independent of the base temperature and so only changes of the
temperature are considered in the aforementioned temperature compensation
mechanism.

[0026] FIG. 3 is a schematic diagram illustrating yet another embodiment
of the improved optical instrument according to some embodiments of the
present invention. According to this embodiment, temperature compensation
member 150 is connected on one end to housing 110 which houses the lenses
112A-E and on the other hand, via a securing member 330 to bore 130. A
gauge member 330 is connected to securing member 330 whereas a
corresponding stopper 320 is attached to temperature compensation member
150. Both gauge member 330 and stopper 320 are located and shapes such
that gauge member 330 by physical contacting stopper 320, limits the
thermal expansion of temperature compensation member 150. The point from
which the thermal expansion is limited as well as the direction of the
limit on the thermal expansion may be determined in accordance with the
specific design of the optical instrument 100.

[0027] Advantageously, limiting the thermal expansion of temperature
compensation member 150 beyond a predefined threshold may be beneficial
if, for example the expansion is counterproductive for the focal length
compensation purposes. This may be cause, for example, due to a
non-linear behavior of the focal length of lenses 112A-E as a function of
the temperature. Thus, the limiting of the expansion enables to benefit
from the compensation mechanism up until a point that the expansion
undermines the focal length compensation.

[0028] It is understood that limiting of the expansion may be in various
ways. For example: (i)it may be fully asymmetric--enabling expansion on
one direction only--with no thermal expansion whatsoever on the other
direction. (ii) It may limit expansion beyond a certain point on any
direction or both and (iii) it may also apply some force against the
expansion, for example by a spring (no shown) so as to reduce the thermal
expansion but not enough to stop it altogether. The use of the
abovementioned options may provide the designer of optical instrument 100
with the required degrees of freedom to optimize the focal length
compensation mechanism given the practical non-linearity effects of
lenses 112A-E. It is also should be noted, from a structural point of
view, that gauge member 330 may be attached directly to bore 130 so that
stopper 320 is limited directly by a protruding member from bore 130.

[0029] In some embodiments the stopper is attached to the temperature
compensation member and may be located such as to limit the displacement
of the set of lenses in at least one direction along the optical axis.
The stopper may be located in a predefined location relative to the set
of lenses so as to enable displacement of the set of lenses in at least
one direction along the optical axis only to a certain point. The stopper
may be configured to apply a force so as to reduce the displacement of
the set of lenses along the optical axis.

[0030] In the above description, an embodiment is an example or
implementation of the inventions. The various appearances of "one
embodiment," "an embodiment" or "some embodiments" do not necessarily all
refer to the same embodiments.

[0031] Although various features of the invention may be described in the
context of a single embodiment, the features may also be provided
separately or in any suitable combination. Conversely, although the
invention may be described herein in the context of separate embodiments
for clarity, the invention may also be implemented in a single
embodiment.

[0032] Reference in the specification to "some embodiments", "an
embodiment", "one embodiment" or "other embodiments" means that a
particular feature, structure, or characteristic described in connection
with the embodiments is included in at least some embodiments, but not
necessarily all embodiments, of the inventions.

[0033] It is to be understood that the phraseology and terminology
employed herein is not to be construed as limiting and are for
descriptive purpose only.

[0034] The principles and uses of the teachings of the present invention
may be better understood with reference to the accompanying description,
figures and examples.

[0035] It is to be understood that the details set forth herein do not
construe a limitation to an application of the invention.

[0036] Furthermore, it is to be understood that the invention can be
carried out or practiced in various ways and that the invention can be
implemented in embodiments other than the ones outlined in the
description above.

[0037] It is to be understood that the terms "including", "comprising",
"consisting" and grammatical variants thereof do not preclude the
addition of one or more components, features, steps, or integers or
groups thereof and that the terms are to be construed as specifying
components, features, steps or integers.

[0038] If the specification or claims refer to "an additional" element,
that does not preclude there being more than one of the additional
element.

[0039] It is to be understood that where the claims or specification refer
to "a" or "an" element, such reference is not be construed that there is
only one of that element.

[0040] It is to be understood that where the specification states that a
component, feature, structure, or characteristic "may", "might", "can" or
"could" be included, that particular component, feature, structure, or
characteristic is not required to be included.

[0041] The descriptions, examples, methods and materials presented in the
claims and the specification are not to be construed as limiting but
rather as illustrative only.

[0042] Meanings of technical and scientific terms used herein are to be
commonly understood as by one of ordinary skill in the art to which the
invention belongs, unless otherwise defined.

[0043] The present invention may be implemented in the testing or practice
with methods and materials equivalent or similar to those described
herein.

[0044] Any publications, including patents, patent applications and
articles, referenced or mentioned in this specification are herein
incorporated in their entirety into the specification, to the same extent
as if each individual publication was specifically and individually
indicated to be incorporated herein. In addition, citation or
identification of any reference in the description of some embodiments of
the invention shall not be construed as an admission that such reference
is available as prior art to the present invention.

[0045] While the invention has been described with respect to a limited
number of embodiments, these should not be construed as limitations on
the scope of the invention, but rather as exemplifications of some of the
preferred embodiments. Other possible variations, modifications, and
applications are also within the scope of the invention.

Patent applications by Shimon Aburmad, Nahariya IL

Patent applications by OPGAL OPTRONIC INDUSTRIES LTD.

Patent applications in class With temperature compensation or control

Patent applications in all subclasses With temperature compensation or control